This invention relates to acrylate based anaerobic curing compositions which are storage stable. Anaerobic curing compositions, if continually exposed to an adequate supply of air or oxygen, remain in an uncured state over long periods of time. However, once the air or oxygen is excluded, these compositions rapidly cure. Depending on the formulation of the compositions, they may be used as anaerobic adhesives or anaerobic sealants.
Anaerobic curing compositions which can be used as adhesives or sealants are well Known in the art. Typical anaerobic curing compositions are described in U.S. Pat. Nos. 2,895,950 (Krieble), 3,043,820 (Krieble) and 3,218,305 (Krieble).
The characteristic of premature polymerization in oxygen-free environments can cause problems in packaging anaerobic curing compositions. At present, one option has been to package anaerobic curing compositions in air permeable containers with large amounts of air trapped in the package. For example, to package one liter of product, a two liter container is used. This is both expensive and ecologically wasteful.
Another option has been to design packages to maximize the surface area between the anaerobic composition and the available air space. For example, currently packaging is done in long, thin, air permeable cartridges. This allows all areas of the product to be exposed to air. However, packages of such design can only hold small quantities of product and are not feasible for packaging bulk amounts.
Several solutions have been proposed to keep these anaerobically curing compositions from prematurely polymerizing. For instance, U.S. Pat. No. 2,628,178 discloses bubbling air through the composition. The problem is that this aeration would have to be continuous, and is therefore not feasible for packaging purposes. In U.S. Pat. No. 3,795,641, aeration was done in the presence of tertiary amines and compounds containing an imido group. It is believed that these compounds play a catalytic role in creating hydroperoxy sites along the backbone of the polyethylene glycol dimethacrylate. It is also believed that the aeration actually increases the level of dissolved oxygen in the composition. To achieve suitable shelf life, aeration times of at least 2 to 4 days were necessary.
In view of the foregoing, there is a continuing need in the anaerobic curing composition art for rapid and inexpensive methods to prevent premature polymerization. Also, there is a need for being able to package anaerobic compositions in bulk containers such as 5 liter pails and to increase the shelf stability of these compositions.